1. Field of the Invention
The present invention relates to providing a seal between a stationary housing and a stripper rubber constructed to snugly receive a drill string-passed in a well casing for a well bore, and, more particularly, to the provision of a sealing gasket constructed and arranged for compressing an elastic seal material in a truncated conical cavity between such a stationary housing and steel core secured to such a stripper rubber.
2. Description of the Prior Art
Oil, water and gas wells are drilled with a drill bit attached to a hollow drill string which passes through a well casing installed in the well bore. A drilling head is usually attached to the top of the well casing where it emerges from the ground to seal the interior of the well casing from the surface and thereby permit the forced circulation of drilling fluid or gas during drilling operations. In the more commonly-used forward circulation drilling mode, the drilling fluid or gas is pumped down through the interior of the hollow drill string, out the bottom thereof, and upward through the annulus between the exterior of the drill string and the interior of the well casing. In reverse circulation, the drilling fluid or gas is pumped down the annulus between the drill string and the well casing and then upward through the hollow drill string.
The drilling head typically includes a stationary body to support a spindle that is rotated by a kelly for the rotary drilling operation. A seal often referred to as a stripper packer, is carried by the spindle to seal the periphery of the kelly or the sections of drill pipe, whichever is passing through the spindle, and thereby confine the fluid pressure in the well casing and prevent the drilling fluid, whether liquid or gas, from escaping between the rotary spindle and the drill string. The rotation of the kelly and drill string is accompanied by frequent upward and downward movement of the kelly and drill string as required for the addition of drill pipe sections. The high pressure fluid supplied to the drilling head requires that the stripper packing in the drilling head withstand continuous flexing of the rubber mass engaged with the kelly or drill string. When the drilling of a well proceeds to greater depths, and may also include the use of air as the drilling fluid, the effective sealing with long continued integrity is important to prevent unwanted release of the drilling fluid under the necessary higher pressure.
The arrangement of parts used to maintain the integrity of the sealed condition of the parts associated with the attachment of the stripper packer at the rotary spindle has been a source of problems involving the containment of drilling fluid pressure. Typically, the stripper packer includes an elongated generally cylindrical hard-rubber packer having an annular mounting collar secured to its upper end. The mounting collar, in turn, is secured onto the lower end of the rotatable spindle. Often the mounting collar is secured to the stripper packer by being molded integrally therewith. That is, the mounting collar often includes such structural expedients as a radial-projecting lip, a circumferential dovetail keyway, or a plurality of radial through openings onto or through which the stripper rubber is directly molded for a positive mechanical interlock between the mounting flange and the stripper rubber. Some such packers may have been subject to instances of tearing of the stripper rubber or breaking of the fluid seal with the mounting collar due to localized stress concentrations at the rubber to collar interface. Among the known structures are those disclosed in U.S. Pat. Nos. 4,345,769; 3,503,617; 3,400,938; and 2,170,916.
A stripper packer assembly is disclosed in U.S. Pat. No. 4,486,025 having separable mounting collar and a stripper rubber element wherein nut and bolt assemblies dispersed about a bolt circle are used to compressively clamp the stripper rubber in face sealing engagement with an extended formed sealing surface of the mounting collar. The stripper packer is used to provide a fluid pressure-tight seal and to provide for transmission of torque loads from the stripper rubber to the mounting collar.
The sealing relationship between the stripper packer and the mounting collar also includes the use of an O-ring seated in a mounting groove formed in an annular section of the mounting collar. The mounting collar must be passed into a suitably enlarged bore in the rotary spindle and in so doing the O-ring protruding from the periphery of the collar must be compressed to fit in the bore so that the operative position of the O-ring forms an elastic seal with the bore without damage to the O-ring. When the assembling operation must be accomplished at the drilling site, the working conditions are a disadvantage. The immediate area surrounding the drilling head at the drilling site presents a particularly harsh environment for carrying out the required assembly operation for the stripper packer. The ever presents of dirt and encounters with drilling slurry increase the difficult but necessary alignment of parts to form the seal in the stripper packer. These conditions are especially acute when assembling an o-ring type seal. An intended sealed relation between the parts forming the stripper packer is often discovered by the occurrence of the leakage to the site of the sealing surface only after commencing the drilling operation thus prolonging costly downtime. The art has not produced many viable alternatives to the above-described structures to provide a sealed condition between the stripper rubber and the housing of the drill head due, in part, to the difficulty of forming suitable releasable connection between a mounting collar and a stripper rubber. This has been particularly true in those cases where the frictional engagement between the stripper rubber and the drill string provides the rotary driving force for the rotary spindle in the drilling head. In such instances, the stripper rubber is under constant torque loading and this tends to accelerate wear and ultimate failure of the rubber-to-mounting collar seal.
Accordingly, it is an object of the present invention to provide a gasket face protruding from the truncated conical load bearing surface of a steel core-used also to mount a stripper rubber thereto.
It is a further object of the present invention to provide an elastic sealing gasket for compressing against a truncated conical surface disposed between a stationary housing and stripper rubber forming part of a drilling head.